Prepared in cooperation with the IDAHO DEPARTMENT OF WATER RESOURCES WASHINGTON STATE DEPARTMENT OF ECOLOGY UNIVERSITY OF IDAHO WASHINGTON STATE UNIVERSITY Ground-Water Flow Model for the Spokane Valley-Rathdrum Prairie Aquifer, Spokane County, Washington, and Bonner and Kootenai Counties, Idaho Scientific Investigations Report 2007–5044 U.S. Department of the Interior U.S. Geological Survey Cover: Photograph of Spokane Valley, Washington. The U.S. Geological Survey streamflow gaging station on the Spokane River at Greenacres, Washington, is to the right (upstream) of where Barker Road Bridge crosses the river. (Photograph taken by Paul Hsieh, U.S. Geological Survey, 2005.) Ground-Water Flow Model for the Spokane Valley-Rathdrum Prairie Aquifer, Spokane County, Washington, and Bonner and Kootenai Counties, Idaho By Paul A. Hsieh, Michael E. Barber, Bryce A. Contor, Md. Akram Hossain, Gary S. Johnson, Joseph L. Jones, and Allan H. Wylie Prepared in cooperation with the Idaho Department of Water Resources, Washington State Department of Ecology, University of Idaho, and Washington State University Scientific Investigations Report 2007–5044 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior DIRK KEMPTHORNE, Secretary U.S. Geological Survey Mark D. Myers, Director U.S. Geological Survey, Reston, Virginia: 2007 For product and ordering information: World Wide Web: http://www.usgs.gov/pubprod Telephone: 1-888-ASK-USGS For more information on the USGS--the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1-888-ASK-USGS Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. Suggested citation: Hsieh, P.A., Barber, M.E., Contor, B.A., Hossain, Md. A., Johnson, G.S., Jones, J.L., and Wylie, A.H., 2007, Ground-water flow model for the Spokane Valley-Rathdrum Prairie Aquifer, Spokane County, Washington, and Bonner and Kootenai Counties, Idaho: U.S. Geological Survey Scientific Investigations Report 2007-5044, 78 p. iii Contents Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................2 Purpose and Scope ..............................................................................................................................2 Description of Study Area ...................................................................................................................4 Previous Investigations........................................................................................................................4 Hydrology of Aquifer......................................................................................................................................5 Geologic Setting ....................................................................................................................................5 Areal Extent............................................................................................................................................6 Vertical Extent .......................................................................................................................................8 Hydraulic Properties.............................................................................................................................9 Horizontal Hydraulic Conductivity ...........................................................................................10 Vertical Hydraulic Conductivity ...............................................................................................12 Specific Yield ..............................................................................................................................12 Inflows to Aquifer................................................................................................................................12 Precipitation................................................................................................................................13 Tributary Basins and Adjacent Uplands .................................................................................16 Lakebed Seepage and Surface Overflow ..............................................................................18 Losing Segments of Spokane River ........................................................................................20 Return Percolation from Irrigation ..........................................................................................20 Effluent from Septic Systems ...................................................................................................20 Outflows from Aquifer ........................................................................................................................23 Withdrawals from Wells ...........................................................................................................23 Gaining Segments of Spokane River ......................................................................................26 Little Spokane River ...................................................................................................................26 Subsurface Outflow ...................................................................................................................27 Interaction Between Aquifer and Spokane River .........................................................................28 Ground-Water Levels and Movement .............................................................................................32 Ground-Water Flow Model .........................................................................................................................41 Spatial Discretization .........................................................................................................................41 Temporal Discretization .....................................................................................................................41 Boundary Conditions and Implementation of MODFLOW Packages .........................................44 Recharge Package ....................................................................................................................44 Well Package ..............................................................................................................................44 Flow and Head Boundary Package ........................................................................................44 River Package.............................................................................................................................44 Streamflow-Routing Package ..................................................................................................45 General-Head Boundary Package ..........................................................................................47 Hydraulic Conductivity .......................................................................................................................47 Specific Yield .......................................................................................................................................50 iv Contents—Continued Model Calibration.........................................................................................................................................52 Nonlinear Least-Squares Regression Method ..............................................................................52 Calibration Data...................................................................................................................................52 Weights for Measured Quantities ....................................................................................................53 Estimated Parameters ........................................................................................................................54 Assessment of Calibration ................................................................................................................56 Simulated Flows in Aquifer ...............................................................................................................67 Alternative Models .............................................................................................................................68 Model Limitations and Suggestions for Future Work ............................................................................73 Summary and Conclusions .........................................................................................................................73 Acknowledgments .......................................................................................................................................75 References Cited..........................................................................................................................................75 Figures Figure 1. Map showing location of the Spokane Valley-Rathdrum Prairie aquifer, Spokane County,